Re: [libvirt PATCH v2 39/56] util: import an event loop impl based on GMainContext

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On Fri, Jan 31, 2020 at 03:48:06PM +0100, Pavel Hrdina wrote:
> On Tue, Jan 28, 2020 at 01:11:20PM +0000, Daniel P. Berrangé wrote:
> > The libvirt-glib project has provided a GMainContext based
> > event loop impl for applications. This imports it and sets
> > it up for use by libvirt as the primary event loop. This
> > remains a private impl detail of libvirt.
> > 
> > IOW, applications must *NOT* assume that a call to
> > "virEventRegisterDefaultImpl" results in a GLib based
> > event loop. They should continue to use the libvirt-glib
> > API gvir_event_register() if they explicitly want to
> > guarantee a GLib event loop.
> > 
> > This follows the general principal that the libvirt public
> > API should not expose the fact that GLib is being used
> > internally.
> > 
> > Signed-off-by: Daniel P. Berrangé <berrange@xxxxxxxxxx>
> > ---
> >  build-aux/syntax-check.mk |   2 +-
> >  po/POTFILES.in            |   1 +
> >  src/libvirt_private.syms  |   5 +
> >  src/util/Makefile.inc.am  |   2 +
> >  src/util/vireventglib.c   | 455 ++++++++++++++++++++++++++++++++++++++
> >  src/util/vireventglib.h   |  28 +++
> >  6 files changed, 492 insertions(+), 1 deletion(-)
> >  create mode 100644 src/util/vireventglib.c
> >  create mode 100644 src/util/vireventglib.h
> 
> [...]
> 
> > diff --git a/src/util/vireventglib.c b/src/util/vireventglib.c
> > new file mode 100644
> > index 0000000000..be057c8e3c
> > --- /dev/null
> > +++ b/src/util/vireventglib.c
> > @@ -0,0 +1,455 @@
> > +/*
> > + * vireventglib.c: GMainContext based event loop
> > + *
> > + * Copyright (C) 2008 Daniel P. Berrange
> > + * Copyright (C) 2010-2019 Red Hat, Inc.
> > + *
> > + * This library is free software; you can redistribute it and/or
> > + * modify it under the terms of the GNU Lesser General Public
> > + * License as published by the Free Software Foundation; either
> > + * version 2.1 of the License, or (at your option) any later version.
> > + *
> > + * This library is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > + * Lesser General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU Lesser General Public
> > + * License along with this library. If not, see
> > + * <http://www.gnu.org/licenses/>.
> > + */
> > +
> > +#include <config.h>
> > +
> > +#include <stdio.h>
> > +#include <string.h>
> > +#include <stdlib.h>
> > +
> > +#include "vireventglib.h"
> > +#include "vireventglibwatch.h"
> > +#include "virerror.h"
> > +#include "virlog.h"
> > +
> > +#ifdef G_OS_WIN32
> > +# include <io.h>
> > +#endif
> > +
> > +#define VIR_FROM_THIS VIR_FROM_EVENT
> > +
> > +VIR_LOG_INIT("util.eventglib");
> > +
> > +struct virEventGLibHandle
> > +{
> > +    int watch;
> > +    int fd;
> > +    int events;
> > +    int removed;
> > +    guint source;
> > +    virEventHandleCallback cb;
> > +    void *opaque;
> > +    virFreeCallback ff;
> > +};
> > +
> > +struct virEventGLibTimeout
> > +{
> > +    int timer;
> > +    int interval;
> > +    int removed;
> > +    guint source;
> > +    virEventTimeoutCallback cb;
> > +    void *opaque;
> > +    virFreeCallback ff;
> > +};
> > +
> > +static GMutex *eventlock;
> > +
> > +static int nextwatch = 1;
> > +static GPtrArray *handles;
> > +
> > +static int nexttimer = 1;
> > +static GPtrArray *timeouts;
> > +
> > +static gboolean
> > +virEventGLibHandleDispatch(int fd G_GNUC_UNUSED,
> > +                           GIOCondition condition,
> > +                           gpointer opaque)
> > +{
> > +    struct virEventGLibHandle *data = opaque;
> > +    int events = 0;
> > +
> > +    if (condition & G_IO_IN)
> > +        events |= VIR_EVENT_HANDLE_READABLE;
> > +    if (condition & G_IO_OUT)
> > +        events |= VIR_EVENT_HANDLE_WRITABLE;
> > +    if (condition & G_IO_HUP)
> > +        events |= VIR_EVENT_HANDLE_HANGUP;
> > +    if (condition & G_IO_ERR)
> > +        events |= VIR_EVENT_HANDLE_ERROR;
> > +
> > +    VIR_DEBUG("Dispatch handler %p %d %d %d %p", data, data->watch, data->fd, events, data->opaque);
> 
> Missing names for the formatted data:
> 
> "Dispatch handler data=%p watch=%d fd=%d evetns=%d opaque=%p".
> 
> The same thing is done for timer and it improves the debug log.
> 
> There are some more places that should be fixed [1].

Yep.

> > +static int
> > +virEventGLibHandleAdd(int fd,
> > +                      int events,
> > +                      virEventHandleCallback cb,
> > +                      void *opaque,
> > +                      virFreeCallback ff)
> > +{
> > +    struct virEventGLibHandle *data;
> > +    GIOCondition cond = 0;
> > +    int ret;
> > +
> > +    g_mutex_lock(eventlock);
> > +
> > +    data = g_new0(struct virEventGLibHandle, 1);
> > +
> > +    if (events & VIR_EVENT_HANDLE_READABLE)
> > +        cond |= G_IO_IN;
> > +    if (events & VIR_EVENT_HANDLE_WRITABLE)
> > +        cond |= G_IO_OUT;
> 
> Aren't we missing VIR_EVENT_HANDLE_ERROR and VIR_EVENT_HANDLE_HANGUP?

Yes & I'll pull this into helper methods to avoid repeating it.

> > +    if (events) {
> > +        GIOCondition cond = 0;
> > +        if (events == data->events)
> > +            goto cleanup;
> > +
> > +        if (data->source) {
> 
> I would change the condition to "data->source != 0" to be consistent
> with other checks in this file and we also prefer this form in the
> case where the value is not boolean or pointer.  There are more places
> that should be fixed as well. [2]

Ok

> > +{
> > +    GMainContext *ctx = g_main_context_default();
> > +
> > +    if (!g_main_context_acquire(ctx)) {
> > +        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> > +                       _("Another thread has acquired the main loop context"));
> > +        return -1;
> > +    }
> > +
> > +    g_main_context_iteration(ctx, TRUE);
> > +
> > +    g_main_context_release(ctx);
> 
> No need to acquire and release the GMainContext here as it's done by
> g_main_context_iteration() as well.  In case you want to have the
> explicit error some comment would be nice.

Yeah it is redundant.


I also need to include the systemtap probe points we have in the current
glib impl

Regards,
Daniel
-- 
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